Replacing light fixture, old wires

9 years ago

I am trying to replace an old ceiling light fixture in my 1949 house, which I was hoping would be a simple job. The power is off as d old fixture is loose, but the wiring is a little more complicated than I anticipated. The old fixture has one yellow and one brown wire, both insulated with cloth fabric instead of plastic. In the ceiling there are four wires three of them are connected into the brown wire on the old fixture and one is connected to the yellow wire on the old fixture. I want to be absolutely sure that I am connecting the new fixture correctly. Can anyone give some advice on which wires should be connected to the black and white wires on the new outlet? Thanks!

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Comments (3)

kudzu9
9 years ago
The wire in your picture that looks reddish should be the hot, which is connected to the black wire in the fixture. The bundle of three whitish wires should be the neutrals and be connected to the white fixture wire. (I say this with a 99% likelihood...it's always best to check with a multimeter, especially on old wiring).

Not surprisingly, it appears that you don't have a ground wire. However, if that metal box has armored cable running to it, the box may be grounded and you could connect a fixture ground wire to it. Armored cable is a spiral metal wrap, and, when I look at your picture, it's possible that I'm seeing the end of an armored cable fitting where the wires enter the box.

All of these things -- that the reddish wire is the hot and whether the box is grounded -- could be determined in about a minute by someone who had a meter and knew how to use it.
btharmy
9 years ago
The armor of old BX cable is not rated as an equipment ground. It doesn't matter if you get an indication that the box is grounded through the cable jacket. It may be "connected" to ground but is not "properly grounded" and will fail in the event of a fault condition.
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joefixit2
9 years ago
To re-iterate what btharmy said, the old BX has no bonding strip and although it may test as being grounded, the resistance of this grounding path will vary greatly depending on the distance of the run and the integrity of the connectors. Once the resistance reaches a level high enough to reduce the flow of fault current to a level below the fuse or circuit breaker rating and a ground fault occurs, the armor will just sit there energized, along with anything else connected to it. Depending on the resistance it can turn into a heating element and get hot enough to start fires, as the high resistance will prevent the fuse from blowing but can allow enough current to flow to create a heater.

For this reason I consider the old BX to be more dangerous than knob & tube, especially as it ages and gets monkeyed with.

Incidentally if you read the label on any new UL approved lighting fixture you will see that it forbids installation on older building wire due to it's insufficient temperature rating.

This post was edited by joefixit2 on Sun, Jan 18, 15 at 9:46